Tropical Cyclone Anggrek Intensifies to Equivalent of Cat. 4 Hurricane

Tropical Cyclone Anggrek intensified to the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale over the South Indian Ocean far to the south of Diego Garcia on Sunday. At 4:00 p.m. EST on Sunday the center of Tropical Cyclone Anggrek was located at latitude 22.2°S and longitude 72.7°E which put it about 1010 miles (1625 km) south of Diego Garcia. Anggrek was moving toward the west-southwest at 18 m.p.h. (29 km/h). The maximum sustained wind speed was 130 m.p.h. (210 km/h) and there were wind gusts to 160 m.p.h. (260 km/h). The minimum surface pressure was 950 mb.

Tropical Cyclone Anggrek was small, but powerful. A circular eye with a diameter of 17 miles (28 km) was at the center of Anggrek’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms revolved around the core of Anggrek’ circulation. Storms near the core generated upper level divergence that pumped mass away from the tropical cyclone. The upper level divergence pumped away more mass than was converging in the lower levels of Tropical Cyclone Anggrek. The removal of mass caused the surface pressure to decrease.

The small circulation around Tropical Cyclone Anggrek was very symmetrical. Winds to hurricane/typhoon force extended out 25 miles (40 km) from the center of Anggrek’s circulation. Winds to tropical storm force extended out 100 miles (160 km) from the center of circulation. The Hurricane Intensity Index (HII) for Tropical Cyclone Anggrek was 25.1. The Hurricane Size Index (HSI) was 8.7 and the Hurricane Wind Intensity Size Index (HWISI) was 33.8.

Tropical Cyclone Anggrek will move through an environment favorable for a strong tropical cyclone during the next 24 hours. Anggrek will move over water where the Sea Surface Temperatures are near 28°C. It will move under the axis of an upper level ridge over the South Indian Ocean. The upper level winds are weak near the axis of the ridge and there will be little vertical wind shear. Tropical Cyclone Anggrek intensify during the next 24 hours. However, if the inner end of a rainband wraps around the existing eye and eyewall, then concentric eyewalls could form. If concentric eyewalls form, then an eyewall replacement cycle could cause Anggrek to start to weakeny.

Tropical Cyclone Anggrek will move around the western part of a high pressure system over the South Indian Ocean. The high pressure system will steer Anggrek toward the south during the next 24 hours. On its anticipated track, Tropical Cyclone Anggrek will move farther away from Diego Garcia.